Pointing device like a mouse, a trackball, a touchpad, a joystick, and so on is a powerful input tool for a computer system. Pointing device detects user's motion through the mechanical, optical, or electronic or combinations of these techniques. Conventional system usually cannot be used for three-dimensional purpose. Until now, some techniques or devices for three-dimensional pointing device are proposed or commercialized. The followings are some of the examples.
Combining two-dimensional pointing devices with other device such as a keyboard or other pointing device is one method for obtaining the three-dimensional point function. This method is less perceivable and requires a great effort to learn and manipulate. Some other methods are more convenient because these methods use a three-dimensional detecting system.
First example is an acoustic three dimensional positioning method using distance measurement between a microphone source and multiple speakers which transmit ultrasonic signal as described in U.S. Pat. No. 5,963,197. The time delays among the speakers determine the position of the pointing device. This acoustic method can be susceptible to echoes, sound speed variation through different environmental conditions, and ultrasonic interference.
A magnetic three-dimensional positioning method is a very popular one in the virtual-reality environments. Three orthogonal electromagnetic coils generate a magnetic filed in the three-dimensional space and a movable sensor in the pointing device detects the field intensity and gradient to determine the position in the three-dimensional magnetic fields as described in U.S. Pat. No. 6,509,888. Interference between the magnetic fields and other materials around the system makes the exact positioning to be difficult. Even the computer system itself generates a magnetic field and interferes with this kind of pointing device.
Optical three-dimensional positioning method uses multiple image sensors and emitters.
In a pointing device, an object emits or reflects lights so that the image sensors can detect the object. The position is calculated by camera imaging algorithms. One example is direct linear transform which provides three-dimensional positions from two-dimensional image data taken by two-dimensional camera. In this system an image sensor captures ambient images without light sources and the image processing method is applied to determine the relative movement of the object as described in U.S. Pat. No. 6,765,555. Currently available three-dimensional positioning devices discussed above or other methods require some specific environment and a large space due to the multiple transmitters and receivers. These constraints are the major obstacles for the applications of three-dimensional pointing devices for most applications which need a pointing device.